1. Field of the Invention
The present invention relates to a display apparatus using a light emitting element in a display pixel, and more particularly to a display apparatus using an organic electroluminescence (EL) element as the light emitting element.
2. Related Art
The organic EL element, which is the light emitting element, takes a laminated structure of laminating in order of an anode, an EL layer and a cathode, on a substrate. When a voltage is applied between the anode and the cathode, holes and electrons are injected into the EL layer, and the EL layer performs electroluminescence. An EL element designed to perform a display by the transmission of the substrate, on which the organic EL element is provided, of a light produced by the light emission of the EL layer is called as a bottom emission type EL element. On the other hand, an EL element designed to perform a display by the light emission to the outside from the opposite side of the substrate, on which the organic EL element is provided, is called as a top emission type EL element.
On the other hand, organic EL displays to use the organic EL elements are roughly classified into passive drive system organic EL displays and active matrix drive system organic EL displays. The active matrix drive system organic EL displays severally have extremely superior display characteristics, such as very high contrast, a wide view angle characteristic, and a superior moving image characteristic.
Moreover, also as for power consumption, the organic EL display is a self light emitting device, and can achieve the reduction of power consumption thereof by controlling the displaying and lighting rate (average picture level) thereof. Furthermore, if the processing of changing the brightness of maximum gradation, for example, between the time of using the organic EL display and the time of waiting the use thereof (automatic brightness control (ABC)) is performed by providing a dimmer function (automatic light control function), then the electric power to be consumed for the light emission of the organic EL element can be suppressed.
The active matrix drive system organic EL display is provided with one or a plurality of thin film transistors per pixel, and the organic EL display makes the organic EL element emit a light by means of the thin film transistors. For example, the display is provided with two thin film transistors per pixel, wherein the thin film transistors include a drive transistor for flowing a current through the organic EL element by receiving the application of a signal voltage according to display data at the gate electrode of the drive transistor and a selection transistor for performing switching for supplying the signal voltage according to the display data to the gate electrode of the drive transistor.
Now, the current to make the organic EL element emit a light has a difference in, for example, two or more digits between the current value necessary for a time when each of the pixels of the organic EL display emits lights at a maximum brightness when in a high brightness display mode and the current value necessary for a time when in a low brightness display mode at a dimmer time. Consequently, if a drive circuit that generates a power source voltage or the like to be supplied to the pixels is designed to generate a voltage necessary for the time of the high brightness display mode, then the power consumption of the drive circuit at a low brightness display mode at a dimmer time may not be reduced sufficiently. Particularly, in the case of an application in which the use of the drive circuit on the low brightness at a dimmer time is a normal state, power consumption at a dimmer time should be reduced.